1. Field of the Invention
The present invention relates generally to chamber closure apparatus used in semiconductor processing apparatus and more particularly to a slit valve closure and associated actuating and control system and method.
2. Brief Description of the Prior Art
Various types of semiconductor manufacturing equipment are used to process semiconductor wafers during the manufacturing of integrated circuits (IC's). For example, chemical vapor deposition (CVD) systems are used to deposit insulating and non-insulating layers over a wafer, plasma etch systems are used to etch a wafer or a layer formed over the wafer, and physical vapor deposition or "sputter" systems are used to physically deposits conductive layers over a wafer. These various processes are usually performed within sealed processing chambers so that the processing conditions can be tightly controlled.
A common way of putting a wafer into a processing chamber and then subsequently removing it is to provide a "slit valve" in a wall of the processing chamber. An elongated, usually horizontal, aperture is formed in the wall. The aperture is sufficiently wide and high to permit the passage of a semiconductor wafer supported by the blade of a robotic wafer handling arm, and is surrounded by a valve seat. An elongated valve closure selectably engages the seat to close the aperture or disengages from the seat to open the aperture.
When the slit valve is closed, a gas-tight seal is required in order to isolate the chamber from external influences. This usually requires an elastomeric gasket or seal, such as an O-ring seal, disposed between the valve seat and the closure. Since the pressure on one side of the slit valve can be as high as atmospheric pressure, while the pressure on the other side of the slit valve can be as low as 10.sup.-8 torr, one atmosphere or more of pressure is often applied to the closure to ensure that the slit valve does not leak even under the most adverse of conditions. This amount of pressure tightly compresses the O-ring seal between the closure door and the valve seat.
It is very important to minimize sources of contamination in semiconductor manufacturing equipment. Even very small particles on the order of 0.2 microns can damage an IC device being created on a semiconductor wafer. A problem encountered with prior art slit valves is that, under high pressures, the elastomeric material of the O-ring is compressed into the metal surfaces of the valve seat and closure such that, when the slit valve is opened, the O-ring is ripped from the metal surface of either the valve seat or the closure, thereby creating a large cloud of particles which can settle on a wafer, on surrounding surfaces, or remain suspended for a considerable period of time. Particles that eventually settle onto the active surface of the wafer can greatly reduce the yield of usable integrated circuits from that wafer.
The problem of particle cloud generation during slit valve opening is of even greater concern with the advent of multiple chamber semiconductor manufacturing equipment. Referring now to FIG. 1, wherein is illustrated a prior art multiple chamber semiconductor processing system 100. The system 100 includes a wafer handling chamber 102, a wafer cassette loading/unloading chamber 104, and a number of wafer processing chambers 106a-106d. The system 100 is typically designed to process a single wafer 108 at a time within any one of the processing chambers 106.
The wafer handling chamber 102 is provided with a computer controlled robotic wafer handler 110 which can support and move the wafer 108. A typical wafer handler 110 includes a "frog's leg" assembly 112 which is coupled at one end to a motor assembly 114 and, at the other end, to a wafer support blade 116. The motor assembly 114 allows the blade 116 to be rotated around an axis A of the motor assembly 114 and also to be moved radially in and out relative to the axis A as indicated by an arrow 118, by opening and closing the "frog's leg" assembly 112 in the direction of an arrow 120. These two degrees of movement allow the wafer handler 110 to move the wafer 108 into and out of the loading/unloading chamber 104 and the processing chambers 106a-106d.
Wafer handlers, such as the handler 110, are commercially available from such companies as Applied Materials of Santa Clara, Calif.
The wafer handling chamber 102 is pentagonal in shape to accommodate the four processing chambers 106a-106d and the loading/unloading chamber 104. A slit valve assembly is disposed in a wall of each of the chambers 104, 106a-106d. Thus, a slit valve assembly 130a is disposed in a chamber wall 132a that forms a boundary between the handling chamber 102 and the processing chamber 106a. Also, a plurality of slit valve assemblies 130b, 130c, 130d are disposed in chamber walls 132b, 132c, 132d, respectively, that form a boundary between the handling chamber 102 and the other processing chambers 106b, 106c, 106d, respectively. Similarly, a slit valve assembly 130e is disposed in a chamber wall 132e that forms a boundary between the handling chamber 102 and the loading/unloading chamber 104. The slit valve assemblies 130a-130e permit the wafer 108 to pass through the walls 132a-132e, respectively, of the handling chamber 102 into the chambers 106a, 106b, 106c, 106d and 104, respectively. Typically, the wafer handling chamber 102 is evacuated during the wafer handling process by a vacuum pump (not shown).
In operation, a stack of wafers (not shown) is placed within the loading/unloading chamber 104, and the slit valve assembly 130e is opened to permit the handler 110 to remove one or more of the wafers from the loading/unloading chamber 104. The slit valve 130e is then closed and the handling chamber 102 is evacuated.
A slit valve assembly to one of the processing chambers 106a-106d is opened to permit the wafer 108 to be placed on a pedestal 134a-134d, respectively, disposed in the processing chamber. As an example of a multiple processing operation, the wafer 108 is initially provided with an oxide layer and is then etched. Thus, in the initial step, the wafer 108 is to be placed in, for example, chamber 106a which is an oxide CVD chamber. Slit valve 130a is opened and the handler 110 passes the wafer 108 through the opening and places it on the pedestal 134a. Slit valve 130a is then closed and the CVD process is performed. After the completion of the CVD process, the slit valve 130a is opened and the wafer 108 is removed by the handler 110 and the slit valve 130a is closed. In the next processing step, the wafer 108 is etched in a reactive ion etch (RIE) chamber. If chamber 106b is an RIE chamber, slit valve 130b is opened, the handler 110 places the wafer 108 on the pedestal 134b, and the slit valve 130b is closed. After the RIE process is performed, the slit valve 130b is reopened, the handler 110 removes the wafer 108, and the slit valve 130b is closed. After the wafer 108 has been completely processed and it is returned to the loading/unloading chamber 104.
At every step in the process, a corresponding slit valve assembly is opened and closed. Since each slit valve opening creates particles which could potentially contaminate the wafer, it is particularly desirable to minimize the number of particles created with each opening of a slit valve.
In a processing sequence such as described above, the wafer 108 may be exposed at least six times to the particles produced by the opening of a slit valve. If the wafer 108 undergoes additional processing steps, it will be exposed to even more slit valve openings. As the trend towards increasingly complex, multi-chamber semiconductor manufacturing equipment continues, the problem with slit valve contamination will become increasingly troublesome. Furthermore, as the feature widths of integrated circuits decrease, integrated circuit wafers will become even more sensitive to damage from such contamination.